The first man to orbit the Earth was Soviet cosmonaut Yuri Gagarin in 1961.
But technically, he wasn't the first one to enter space.
Just eight months earlier, American Air Force officer Joe Kittinger took the first step by making a perilous expedition past Earth's inner atmosphere, to an altitude of 31km.
16th August 1960
Not in a spacecraft, but in a helium balloon!
Col Joe Kittinger, US Air Force – "This was the first time anybody had ever been to this high an altitude. It was the first time man had ever been in an actual space environment. So I had some concern about what was going to happen."
Kittinger was a participant in Project Excelsior III, a mission to test high altitude bailouts.
Project Excelsior III
He knew more than anyone how dangerous the mission was – on a previous attempt a malfunction in his equipment had caused him to lose consciousness, almost killing him.
No life support systems
Only a pressure suit protected Kittinger
Over the course of 1.5 hours, the Helium balloon attached to Kittinger's gondola passed out of the troposphere, and into the stratosphere, to a height that no human had ever reached.
Troposphere, Up to 20km above ground level
Stratosphere, Up to 50km above ground level
Col Joe Kittinger, US Air Force – "I could see the clouds below and the atmosphere, the...the haze layer. It was a...it was a very profound feeling that I had. The realisation of really just how hostile that environment is and it's only 20 miles above our Earth."
Kittinger passed through the ozone layer
Average temperature at this height: -70°C
After reaching his destination of more than 30km above the Earth, it was a case of now or never.
If Kittinger travelled any higher, his pressure suit wouldn't protect him from the thin atmosphere and extreme cold.
Col Joe Kittinger, US Air Force – "I said my silent prayer, I hit the button to start the cameras working, and I jumped from the gondola. And I turned over on my back and the balloon was racing into the heavens - I mean at a fantastic rate - to me it was just flying away. And what it was, the balloon was standing still and I was the one that was falling, so rapidly."
He free falls for a record breaking four and a half minutes, reaching speeds of almost 1000km/h.
On August 16 1960, when space exploration was still just science fiction, Kittinger travelled to the unknown heights of the stratosphere – and standing on the edge of outer space, took the highest step in the world.